Recently, development of a technology of which an object is to improve reliability from a design to an operation of a system has been performed. For example, PTL 1 discloses a technology of improving the reliability of the system in which a fault tree analysis (which is also referred to as an FTA, hereinafter) is used. By this technology, it is possible to evaluate the reliability of the system by calculating a pre-generation probability of a failure, with respect to a failure event which ought to be avoided to be generated, and a cause event which leads to the failure.